Make a unique array with JavaScript

make-unique-array.js

// Time complexity: n(n - 1) => n^2 - n
const toUniqueArray = async (array) =>
  array.reduce((acc, cur) => {
    if (!acc.find((elem) => elem === cur)) acc.push(cur);
    return acc;
  }, []);

const toUniqueArrayIndex = async (array) => {
  const uniqueIndices = [];
  const uniqueElements = [];

  array.map((cur, idx) => {
    if (!uniqueElements.find((elem) => elem === cur)) {
      uniqueIndices.push(idx);
      uniqueElements.push(cur);
    }

    return true;
  });

  return { indices: uniqueIndices, elements: uniqueElements };
};

// every element of an array should be of the same type
//
// Time complexity:
//    - Copying:            n
//    - Sorting (Timesort): n log n
//    - Uniquely pushing:   n
//
// Total: Amortized 2n + n log n
const toUniqueArrayUnstable = (array, type) => {
  if (array.length <= 1) return [].concat(array);

  // copy existing array
  let sorted = [].concat(array);

  // sort array based on a type
  switch (type) {
    case "number":
      sorted.sort((lhs, rhs) => lhs - rhs);
      break;
    case "string":
      sorted.sort((lhs, rhs) => lhs.localeCompare(rhs));
      break;
    default:
      throw new Error(`Unsupported type: ${type}`);
  }

  let result = [];
  let prv = sorted[0];
  result.push(prv);

  for (let i = 1; i < sorted.length; ++i) {
    if (prv !== sorted[i]) result.push(sorted[i]);
    prv = sorted[i];
  }

  return result;
};

Usage:

const res = await toUniqueArray([6, 2, 1, 4, 6, 9, 1, 2, 5, 3, 3, 5]);
console.log(res);

Output:

[6, 2, 1, 4, 9, 5, 3]